"We're thinking mostly about the nuclear threat," Col. Aviram Hasson, who heads the project, told a conference on Aerial Threats in the Modern Age at the Institute for National Security Studies in Tel Aviv Monday.

"We want to reach a situation in which Israel has a ready defense for any threat, present or future."

Meantime, there was consternation in Israel's defense establishment as a result of an apparent U.S. slip-up in publishing details of classified plans for a heavily protected underground facility that would include four Arrow launch sites.

"If an enemy of Israel wanted to launch an attack against a facility, this would give him an easy how-to guide," one Israel officer complained. "This more than worrying, it's shocking."

Hasson gave no details on how the Arrow 3 development has been speeded up.

But Israeli officials have said for some time the project is aimed at boosting the missile's range and operational altitude to knock out hostile ballistic missiles, carrying either nuclear or conventional warheads, outside Earth's atmosphere to minimize fallout.

The shorter-range Arrow 2 variant currently in service with the Israeli air force, which has responsibility for missile defense, can intercept a ballistic missile at a much lower altitude, in the last phase of the missile's trajectory.

IAI and the air force conducted a successful flight test for Arrow 3 Feb. 25 from the Palmachim air force base on the Mediterranean coast south of Tel Aviv although it did not involve an actual interception.

Arrow 3, which IAI is developing with U.S. aerospace giant Boeing Co., is slated to become operational in 2015-16.

It has a range of 1,500 miles, far greater than that of the Arrow 2 variant now in service.

Once the Arrow 3 breaks free of the Earth's atmosphere, the interceptor breaks away from the launch vehicle and carries out a series of maneuvers in space as it locks onto its target, then rams it in a head-on collision.

Weighing less than half the Arrow 2, Arrow 3 does not need to know the exact location of the target missile when it is launched. It locates the incoming missile once it's in space.

The United States has pledged $250 million toward Israel's acquisition of four Arrow 3 batteries and is expected, despite U.S. defense budget cutbacks, to provide $680 million for a further four batteries.

Future batteries are expected to hold more interceptors than the current models, which will make them more expensive.

Two Arrow 2 batteries are providing the top level of a three-tier Israeli missile defense shield that includes the short-range Iron Dome system, built by Israel's Rafael Advanced Defense Systems, and the medium-range David's Sling weapon being developed by Rafael and the U.S. Raytheon Co.

Arrow 3 will become the top layer once it's operational. The theory is that whatever missiles get past its interceptors will be destroyed by the lower-altitude Arrow 2s.

The Times of Israel reported Tuesday details of the supposedly secret project in the Negev Desert south of Tel Aviv were disclosed, apparently inadvertently, in a tender issued several weeks ago by the U.S. Army Corps of Engineers to U.S. construction firms with security clearances.

These are the only companies that will be allowed to bid on the tender that revealed the $100 million project would have five levels underground and will be nuclear-hardened withstand attacks by weapons of mass destruction.

That indicated that Israel anticipates Iran will have nuclear missile capability by the time the complex, known as Site 911, is completed within two years.

The Times of Israel said Site 911 would be located at the Tal Shahar air base in the Negev. The base is classified as a secret, but it's widely known it lies halfway between Jerusalem and the southern port of Ashdod.

According to the daily, it will have four vertical launch chambers, each to hold six missiles.

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